1. Field of the Invention
The present invention relates generally to a rotary head drum apparatus having rotary and stationary drum members, and more particularly is directed to an arrangement through which signals are transmitted between the stationary drum member and each magnetic head attached to the rotary drum member in a magnetic recording and reproducing apparatus such as a video tape recorder and the like.
2. Description of the Prior Art
A video tape recorder (VTR) generally includes a rotary head drum assembly or apparatus which comprises a rotary drum member having at least one magnetic head attached thereto and a stationary drum member located just below the rotary drum member, with a magnetic tape being helically wrapped around the rotary and stationary drum members. When the rotary drum member is rotated, the magnetic head mounted thereon scans the magnetic tape, thereby effecting the so-called helical scanning. The magnetic head is connected to a rotor of a rotary transformer which transmits signals between the rotary and stationary drum members of the drum assembly.
In a video tape recorder as described above, the magnetic head and the rotor of the rotary transformer have to be electrically connected to each other. For effecting such electrical connection, there has been provided a joint base plate to which there are soldered a lead wire extending from the magnetic or video head and a lead wire extending from a rotor of the rotary transformer. When the magnetic head and the rotor of the rotary transformer are electrically connected by means of the joint base plate, as aforesaid, if the diameter of the rotary drum member is reduced for decreasing the overall size of the VTR, it becomes very difficult to solder the lead wires to the joint base plate in the course of assembling together the various elements of the head drum assembly or apparatus. Further, in the course of the soldering-process, solder flux and solder ball are produced and frequently enter the inside of the head drum.
In order to electrically connect the magnetic head and the rotor of the rotary transformer to each other without employing the joint base plate, it has been proposed to use a connector comprised of a plug pin and a plug socket which, when the head drum apparatus is assembled are electrically connected to each other. However, a relatively large force is required to insert the plug pin into the plug socket so that a load is applied to a bearing or the like. Therefore, a rotary head drum apparatus of this kind is undesirably influenced by such large insertion force which causes the magnetic head initially mounted on the rotary drum with high accuracy to be displaced from its desired position.
Further, in a rotary head drum apparatus of a video tape recorder as described above, the rotary head drum member has to be connected to ground through a cable extending between the head drum and a head amplifier. To ground the head drum, a joint base plate is attached to the lower surface of the stationary drum, for example, by a screw, and a ground contact is connected to the joint base plate. However, when the joint base plate is attached to the lower surface of the stationary drum by a screw for grounding the head drum, the head drum may be deformed thereby so that the tracking accuracy is deteriorated, and the resulting picture is disturbed accordingly.
Further, in a known rotary head drum apparatus, a support shaft has a press fit in a bore of the lower stationary drum member and the upper rotary drum member is rotatably supported by the support shaft via a bearing. In assembling this kind of rotary head drum apparatus, in order to fit the support shaft in the stationary drum member, with high accuracy in the vertical direction, a so-called shrink-fit process is employed. According to such shrink-fit process, the stationary drum member is heated to 150.degree. C. or more so that its bore is diametrically expanded and, while the stationary drum member is in this heated condition, the support shaft is easily fitted into the bore of the stationary drum. Of course, when the stationary drum member cools down to ambient temperature, the bore contracts on the support shaft and seizes the latter. The shrink-fit process has the following advantages. If the support shaft is press-fitted into the bore of the stationary drum member at room temperature, then the support shaft will dig into the inner surface of the bore of the stationary drum member. As a result, the support shaft cannot be precisely axially located in the bore of the stationary drum member. On the other hand, when the stationary drum member is heated so as to temporarily increase the inner diameter of the bore, the support shaft can be fitted into the bore with a small inserting force. Hence, the inner surface of the bore of the stationary drum member can be protected from being scored or cut, and the support shaft can be fitted into the bore with a high degree of accuracy in the axial or vertical direction.
The shrink-fit process, however, cannot avoid the following defects. If the stationary drum is heated in order to fit the support shaft into the bore thereof, as in the shrink-fit process, then the coil of the rotary transformer attached to the stationary drum member may be burned. Further, the shrink-fit process decreases the bonding force of the bonding agent which secures the rotary transformer to the stationary drum member. There is then a possibility that the rotary transformer will be detached from the stationary drum member. Therefore, the shrink-fit process cannot be applied to a rotary head drum apparatus of the type in which the rotary transformer is secured to the stationary drum member by an adhesive or bonding agent.